Conventional powertrains typically include an internal combustion engine that uses reciprocating pistons disposed within corresponding engine cylinders to combust a mixture of fuel and air. The combustion process generates engine torque on a driveshaft, which in turn is delivered to a transmission via a hydrodynamic torque converter or a friction clutch. An output member of the transmission ultimately acts on a load. The load may be in the form of a set of drive wheels when the powertrain is used to power an automotive vehicle, or in the form of a propeller shaft, generator, conveyor, or another load in other powertrain configurations.
In order for the engine to start, an engine flywheel must be rotated from a standstill to above a threshold speed, with the threshold speed being sufficient for initiating an intake of the fuel/air mixture into the cylinders via a fuel delivery system. An operator may request an engine start event by depressing a start button or turning an ignition key, or such a request may be generated autonomously or remotely. The received request closes a solenoid control relay, which in turn causes an electrical current to be delivered to a starter solenoid.
The starter motor has a shaft on which is disposed a translatable pinion gear. The pinion gear is ultimately urged by a lever arm by operation of the starter solenoid into engagement with a mating gear element disposed on the engine flywheel. The starter motor gear is then energized so that torque from the starter motor rotates the engine via the engaged pinion gear and engine flywheel to the threshold speed noted above. Upon release of the ignition key or starter button, the solenoid control relay opens to disconnect the battery from the starter motor and starter solenoid. The starter motor stops and the pinion gear disengages from the flywheel. The internal combustion process is thereafter sustained via operation of the fuel delivery system.
A successful engine starting event thus occurs when a controller, e.g., an engine control module, enables the starter control relay via an electronic enable signal and, after passage of a calibrated duration, the engine starts. However, a “no-start” condition sometimes results even when the starter control relay has been properly enabled. While a faulty starter control relay may be the culprit for such a failure mode, other fault candidates exist, including a faulty battery, starter solenoid, starter motor, or power/grounding wire for the starter motor or solenoid. Other fault candidates include a faulty pinion gear or flywheel, engine, or fuel delivery system. However, conventional diagnostic approaches are typically unable to distinguish one fault mode from the other, which can complicate maintenance and repair efforts.